The present invention concerns lipid vesicles made with materials that would not ordinarily be considered as vesicle formers. More particularly, it has been discovered that N,N-dimethylamides prepared from straight chain carboxylic acids can be formed into lipid vesicles. If the vesicles are in the form of paucilamellar lipid vesicles, these vesicles may have a water-immiscible oily material contained in their amorphous central cavity. Alternatively, the vesicles of the invention may just contain aqueous materials. The preferred materials for making these vesicles are the N,N-dimethylamides of tall oils (DMATO) or soy bean oils (DMASO).
DMATO and other N,N-dimethylamides are used as intermediates, carriers, or active ingredients in the manufacture and/or formulation of a variety of materials, including penetrants, dispersants, solvents and corrosion inhibitors. DMATO has a number of water treatment uses, particularly to control organic deposits and corrosion on surfaces. A particularly valuable use of DMATO is as a solvent or carrier for a variety of oily materials including fungicides.
One of the most important DMATO/fungicide combinations is a dispersion of 2-(thiocyanomethylthio) benzothiazole (TCMTB) in DMATO and organic solvents such as toluene. This combination is used as a fungicide in a variety of industries, including wood preservation, protection of cotton and other agricultural seedlings, and leather tanning.
However, although this combination is very effective, there are many problems associated with its agricultural and manufacturing use. The DMATO/TCMTB dispersion is not stable on its own, but rather requires an organic solvent such as toluene for stability. DMATO is insoluble in water but can be dispersed in water under certain circumstances. Oil-in-water emulsions are not the optimum way of utilizing this fungicide since it does not give an even distribution upon aerosol dispersion. In addition, the use of the organic solvents leads to solvent leaching into the environment, a pollution problem that it is difficult to control. Accordingly, a stable, aqueous dispersible TCMTB/DMATO composition which does not use organic solvents would solve many of these problems.
While lipid vesicles which encapsulate an oily material, such as those disclosed in the U. S. Pat. No. 4,911,928, are now known, the efficacy and long time approval of the DMATO/TCMTB combination makes it important to utilize this formulation. However, one would not expect to be able to make vesicles from DMATO and the other N,N-dimethylamides. Most vesicle formers are in the subclass of amphiphiles which have one end that is highly hydrophilic, e.g., polyoxyethylene or phospho groups, with the other end constituting a highly hydrophobic organic chain such as a long chain fatty acid. DMATO and the other N,N-dimethylamides do not fall within this category since they do not have this hydrophilic head group. The dimethylamides useful in the present invention all have small organic groups (i.e., methyl groups) on the amide nitrogen and only the double bonded oxygen on the neighboring carbon has a possibility of hydrogen bonding. In contrast, the diethanolamides disclosed in the aforementioned U.S. Pat. No. 4,919,928 have two ethanol (--CH.sub.2 CH.sub.2 OH) groups which are highly hydrophilic attached to nitrogen as well as having the double bonded oxygen. These ethanols constitute the highly hydrophilic head groups common in vesicle forming materials.
Accordingly, an object of the invention is to develop a method of delivery for a DMATO/TCMTB system which does not use organic solvents.
Another object to the invention is to provide stable lipid vesicles having N,N-dimethylamides prepared from straight chain carboxylic acids as the major lipid in the bilayer structure of the vesicles.
A further object of the invention is to produce lipid vesicles of N,N-dimethylamides of straight chain carboxylic acids having a water immiscible material encapsulated as the lipid vesicle itself.
A still further object of the invention is to provide a fungicide which is more environmentally neutral than those presently used.
These and other objects and features of the invention will be apparent for the following description and the claims.